Method and apparatus for producing amorphous alloy sheet, and amorphous alloy sheet produced using the same

ABSTRACT

The present invention provides a method for producing a bulk amorphous alloy sheet with high quality at low production cost, by which an alloy melt can be directly transformed into a sheet form without using other additional processes. The method comprises preparing a melt containing alloy components; feeding the melt into a gap defined between two rolls, which rotate in opposite direction to each other, and each of which is provided with heat exchange means; and cooling the melt at a cooling rate higher than the critical cooling rate for transformation of the melt into an amorphous solid phase, when the melt passes through the gap defined between the two rolls. The present invention also provides an apparatus for producing a bulk amorphous alloy sheet with high quality at low production cost, and a bulk amorphous alloy sheet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 National Phase Entry Applicationfrom PCT/KR03/001966, filed Sep. 26, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing an amorphous ornoncrystalline alloy, and more particularly, to a method for producing abulk amorphous alloy sheet.

2. Description of the Related Art

An amorphous alloy is a material that has a liquid phase-likemicrostructure with no crystallinity due to disordered arrangement ofatoms, and contains no crystalline imperfections such as grain boundaryand dislocation, unlike a conventional crystalline alloy. Therefore, anamorphous alloy is a significantly improved material in terms ofmechanical properties such as strength, magnetic properties, corrosionresistance, and the like.

Due to the above-described excellent characteristics, there have beenincreasing interests on amorphous alloy materials, in particular, anamorphous alloy sheet as a new material that can be used for variouspurposes in various industrial fields including the aero-space industry,the nuclear power equipment industry, and the defense industry. However,despite the demands in various industrial fields, there have not yetbeen developments on efficient and industrially applicable methods formass-producing an amorphous alloy sheet.

As for conventional processes for producing amorphous alloys, there aredie casting and permanent mold casting. However, die casting andpermanent mold casting are inappropriate to mass-produce amorphous alloysheets that can be used for various purposes, as well as are not costeffective.

A melt spinning process is another conventional method for the amorphousalloy production. However, since this process is intended for productionof an amorphous alloy material in the form of an ultra-thin strip ofabout 0.05 mm or less in thickness, it is not suitable for production ofa bulk amorphous alloy sheet.

A strip casting process is a process that produces a metal material intoa sheet form. This process has advantages such as equipment investmentcost reduction, low energy consumption, and high proportion of productsrelative to raw materials. However, it has been understood that aconventional strip casting process is not suitable for production of anamorphous alloy sheet, and thus, no reports have been made on examplesof use of a conventional strip casting process for production of anamorphous alloy sheet. Even probabilities that a conventional stripcasting process may be used in production of an amorphous alloy sheethave been denied.

Therefore, in order for a bulk amorphous alloy with good properties tobe used for more various purposes in more various industrial fields,development of a method for mass-producing a bulk amorphous alloy, in asheet form with high utility, at low production cost, is required.

SUMMARY OF THE INVENTION

The present invention provides a method for producing a bulk amorphousalloy sheet with high quality at low production cost, by which an alloymelt can be directly transformed into a sheet form without using otheradditional processes.

The present invention also provides an apparatus for producing a bulkamorphous alloy sheet with high quality at low production cost, and abulk amorphous alloy sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is FIG. 1 is a diagram of a method for producing an amorphousalloy sheet according to the present invention;

FIG. 2 is a schematic view of an apparatus for producing an amorphousalloy sheet according to an embodiment of the present invention;

FIG. 3 is a diagram showing transformation of an amorphous alloy meltinto a sheet form that is carried out in two rolls of the apparatus ofFIG. 2;

FIG. 4 is a diagram showing adjustment of a gap between two rolls in theapparatus of FIG. 2;

FIG. 5 is a diagram showing an example of an arrangement structure oftwo rolls in the apparatus of FIG. 2 according to an angle defined bythe horizontal and a straight line connecting the respective rotationcenters of the two rolls;

FIG. 6 is an X-ray diffraction pattern of an amorphous alloy sheetproduced according to Example of the present invention; and

FIG. 7 is an optical microphotograph of the microstructure of anamorphous alloy sheet produced according to Example of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

A method for producing an amorphous alloy sheet according to the presentinvention comprises: preparing a melt containing alloy components;feeding the melt into a gap defined between two rolls, which rotate inopposite direction to each other, and each of which is provided withheat exchange means; and cooling the melt at a cooling rate higher thanthe critical cooling rate for transformation of the melt into anamorphous solid phase when the melt passes through the gap definedbetween the two rolls.

An apparatus for producing an amorphous alloy sheet according to thepresent invention comprises: a crucible for receiving a melt containingalloy components, which is provided with a melt outlet; two rolls, eachof which is provided with heat exchange means to cool the melt at acooling rate higher than the critical cooling rate for transformation ofthe melt into an amorphous solid phase when the melt passes through agap defined between the two rolls; and a connecting channel for passingthe melt from the melt outlet of the crucible to the gap defined betweenthe two rolls.

Hereinafter, a method for producing an amorphous alloy sheet accordingto the present invention will be described in detail. FIG. 1schematically shows a method for producing an amorphous alloy sheetaccording to the present invention.

The step of preparing a melt can be carried out, for example, using amelting furnace which is provided with heating means suitable formelting alloy components and with a sealable crucible.

The heating means provided in the melting furnace can be operated in aheating manner such as resistance heating, arc heating, inductionheating, infrared heating, e-beam heating, and laser heating, but is notlimited thereto.

The step of preparing a melt can be carried out in an inert or non-inertatmosphere. As for some specific alloys, non-crystallization requires aninert atmosphere. In this case, it is preferable to carry out the stepof preparing a melt in an inert atmosphere.

In a case where the step of preparing a melt is carried out using theaforementioned melting furnace, an inert atmosphere can be accomplishedby feeding an inert gas into the melting furnace. Examples of an inertgas to be used herein include helium, neon, argon, krypton, xenon,radon, nitrogen, or a mixture thereof. Alternatively, an inertatmosphere can be accomplished by maintaining the sealable crucible in avacuum state.

The step of preparing a melt can also be carried out in other specificatmospheres required for specific alloys. In this case, gases requiredfor formation of such specific atmospheres are fed into the crucible.

A melt thus prepared is fed into a gap defined between the two rolls,which rotate in opposite direction to each other, and each of which isprovided with heat exchange means. According to an embodiment of thepresent invention, the melting furnace can have a melt nozzle, which islocated to be near the two rolls. The melt is fed into the gap definedbetween the two rolls through the melt nozzle.

The melt fed into the gap defined between the two rolls is cooled at acooling rate higher than the critical cooling rate for transformation ofthe melt into an amorphous phase. In order to accomplish such rapidcooling, the two rolls may be made of a material with good heatconductivity and may be provided with heat exchange means. Acopper-based alloy material can be used as a good heat conductivematerial for the two rolls, but is not limited thereto. The heatexchange means to be installed in the two rolls may be, for example, acircuit for flow of a cooling fluid, but is not limited thereto. Thecooling fluid may be cooling water or cooling oil.

There are no particular limitations on the diameter and rotation rate ofthe two rolls. However, in view of a heat transfer, a linear velocity atthe circumferences of the two rolls may be in the range of about 1 to 10cm/sec. Also, there are no particular limitations on the gap between thetwo rolls. However, in view of a heat transfer and/or a thickness of adesired sheet, the gap between the two rolls may be in the range ofabout 0.5 to 20 mm. As long as an object of the present invention can beaccomplished, the gap between the two rolls may also be less than about0.5 mm or more than about 20 mm. In addition, there are no particularlimitations on the width of the rolls. The width of the rolls can beappropriately determined depending on the maximum width of a desiredsheet.

Generally, the critical cooling rate for amorphous phase formationvaries depending on types of alloys. An appropriate cooling rate for aspecific alloy can be realized by adjusting the circulation rate of acooling fluid, the rotation rate of the two rolls, the gap between thetwo rolls, the temperature of the melt, etc.

The melt is cast into an amorphous alloy sheet by the above-describedrapid cooling and then removed away from the rolls. Due to rollingeffect by the two rolls, generation of cracks and air gaps is prevented,which was identified by X-ray diffraction and microscope image analysisresults.

In a method of the present invention, if the temperature of the melt tobe fed into the gap defined between the two rolls is too low, meltfeeding is not smoothly carried out, and thus, it is difficult toproduce a sheet. On the other hand, if it is too high, the melt is notsufficiently cooled even using the two rolls and the heat exchangemeans, and thus, it is difficult to produce an amorphous sheet.

If the surface temperature of the two rolls is too low, the melt is notcooled by a uniform proportion, and thus, the loading of the melt is notsmoothly carried out. Furthermore, cracks may be caused in edges of aformed sheet. On the other hand, if it is too high, it is difficult toobtain a cooling rate above the critical cooling rate.

If the rotation rate of the two rolls is too slow, solidification of themelt may be completed before an amorphous solid alloy is completelyremoved away from the rolls, and thus, operation of the rolls may besuspended. On the other hand, if it is too fast, uniform cooling is notsufficiently accomplished, and thus, it is difficult to produce a sheetwith high quality.

If the gap between the two rolls is too small, it is difficult toproduce a bulk amorphous alloy sheet. Furthermore, due to excess feedingof the melt, other process factors may be adversely affected. At thesame time, cracks may be caused in edges of a formed sheet. On the otherhand, if it is too large, a sheet may be formed to an excessivethickness, and thus, a cooling rate above the critical cooling ratecannot be realized at the center portion of a sheet. As a result, it isdifficult to obtain a uniform, high quality amorphous alloy.

By way of an illustrative example, in case of a copper-based amorphousalloy comprised of 45 to 49 atomic % Cu, 32-34 atomic % Ti, 10-13 atomic% Zr, 5-7 atomic % Ni, 1-3 atomic % Sn, and 0.5-2 atomic % Si, thetemperature of the melt to be fed into the gap defined between the tworolls may be set to a range of about 500 to 1,500° C., the surfacetemperature of the two rolls a range of about 15 to 30° C., the rotationrate of the two rolls a range of about 1 to 10 cm/sec, and the gapbetween the two rolls a range of about 0.5 to 20 mm.

It should be understood that the method of the present invention can beapplied to all types of alloys capable of being transformed into anamorphous phase, in addition to the above copper-based alloy.

Hereinafter, an apparatus for producing an amorphous alloy sheetaccording to the present invention will be described in detail. Theapparatus can be efficiently used in production of an amorphous alloysheet according to the above-described method.

An apparatus for producing an amorphous alloy sheet according to thepresent invention comprises: a crucible for receiving a melt containingalloy components and provided with a melt outlet; two rolls, each ofwhich is provided with heat exchange means to cool the melt at a coolingrate higher than the critical cooling rate for transformation of themelt into an amorphous solid phase when the melt passes through a gapdefined between the two rolls; and a connecting channel for passing themelt from the melt outlet of the crucible to the gap defined between thetwo rolls.

FIG. 2 schematically shows an apparatus for producing an amorphous alloysheet comprising a crucible 10, a connecting channel 20, and two rolls30, according to an embodiment of the present invention.

The crucible 10 may be a melting crucible that can control an atmospheretherein. As shown in FIG. 2, the crucible 10 receives a melt containingalloy components and is provided with a melt outlet 18. The crucible 10also comprises a gas supply unit 16 for controlling an atmosphere in thecrucible 10 and a heating unit 14 for melting alloy components toprepare the melt and maintaining the temperature of the prepared melt.

The crucible 10 may further comprise a stopper 12 that can open and shutthe melt outlet 18 to control the release of the melt.

The connecting channel 20 may comprise a heating unit 22 that canmaintain the temperature of the melt in the connecting channel 20 whilethe melt flows from the crucible 10 to the gap defined between the rolls30. The connecting channel 20 may further comprise a gas supply unit 24that can control an atmosphere in the connecting channel 20.

The two rolls 30 may be made of a copper-based alloy containingmaterial. However, since there are no particular limitations on amaterial for the two rolls, the two rolls may also be made of othertypes of materials with good heat conductivity.

Each of the two rolls 30 may comprise a circuit 32 for flow of a coolingfluid as the heat exchange means. The cooling fluid may be cooling wateror cooling oil.

FIG. 3 is a detailed view of the two rolls of FIG. 2 and schematicallyshows transformation of the melt into a solid sheet by cooling when themelt passes through the gap defined between the two rolls. An alloymelt, which can be transformed into an amorphous phase, is fed into thegap defined between the two rolls 30 in rotation, then the melt iscooled while being in contact with the two rolls 30 and cast into asolid sheet. The sheet thus obtained is removed away from the two rolls30 by rotation of the two rolls 30. At this time, in order for thecooling rate of the melt by contact of it with the two rolls 30 to behigher than the critical cooling rate for formation of an amorphousphase, the two rolls 30 is cooled by the heat exchange means. The alloymelt is strongly pressed by the two rolls 30 to cast into an amorphousalloy sheet and then is removed away from the two rolls 30.

If the gap between the two rolls is too small, it is difficult toproduce a bulk amorphous alloy sheet. Furthermore, due to excess feedingof the melt, other process factors may be adversely affected. At thesame time, cracks may be formed at the edges of a formed sheet. On theother hand, if it is too large, a cooling rate above the criticalcooling rate cannot be realized in a center portion of a sheet. As aresult, it is difficult to obtain a uniform, high quality amorphousalloy sheet. In this regard, the gap between the two rolls 30 may be inthe range of about 0.5 to 20 mm. The two rolls may be installed to bespaced apart at a predetermined distance from each other, or may beinstalled in such a way that the gap between the two rolls can beadjusted when needed. FIG. 4 schematically shows adjustment of a gapbetween the two rolls.

FIG. 5 schematically shows the structure of the two rolls arranged insuch a manner that an angle defined by the horizontal and a straightline connecting the respective rotation centers of the two rolls, is inthe range of 0 to 90 degrees. The angle may vary depending oncharacteristics of a melt such as fluidity. For example, if the fluidityof a melt is high, the two rolls can be vertically installed (i.e., theangle is 90 degrees) to smoothly carry out horizontal supply of a meltand release of a sheet. On the other hand, if the fluidity of a melt isinsufficient, the two rolls can be horizontally installed (i.e., theangle is 0 degrees) to smoothly carry out vertical supply of a melt bygravity and release of a sheet. The two rolls may be installed at afixed angle selected from the angle of 0 to 90 degrees or may beinstalled in such a way that the angle can be adjusted in the range.

If the rotation rate of the two rolls is too slow, solidification of amelt may be completed before an amorphous solid alloy is completelyremoved away from the rolls, and thus, operation of the rolls may besuspended. On the other hand, if it is too fast, uniform cooling is notsufficiently accomplished, and thus, it is difficult to produce a sheetwith high quality. In this regard, the two rolls may be installed insuch a way to be operated at a rotation rate of about 1 to 10 cm/sec. Tothis, the two rolls may be connected to conventional driving means (notshown).

Hereinafter, a bulk amorphous alloy sheet according to the presentinvention will be described in detail.

A bulk amorphous alloy sheet according to the present invention iseither a bulk alloy material that consists of fully amorphous phase or abulk alloy material that consists of composite containing amorphous andcrystalline phases.

The term, “bulk sheet” as used herein indicates that an amorphous alloyof the present invention is processed into a material which hasstructural continuity and a relatively large two- or three-dimensionaldimension, not into a thin film (of 100 μm or less in thickness, forexample) dimension. For example, an amorphous alloy sheet of the presentinvention may have a thickness of about 0.5 to 20 mm, but is not limitedthereto. Also, there are no particular limitations on the width, length,and shape of an amorphous alloy sheet of the present invention. Such abulk amorphous alloy sheet can be used for various purposes. Also,attentions have been paid to such a bulk amorphous alloy sheet as a newmaterial in the whole industrial fields including the nuclear powerequipment industry (metal pipe), the defense industry (amorphousmetal-tungsten composite penetrator), the sports equipment industry(golf clubs), and the aero-space industry.

The bulk amorphous alloy sheet according to the present invention can beproduced by the above-mentioned method according to the presentinvention.

The bulk amorphous alloy sheet according to the present invention mayconsist of composite containing amorphous and crystalline phases. Inthat case, the volume or weight ratio of amorphous phase to crystallinephase in the composite can be controlled by varying the processconditions in the above-mentioned method according to the presentinvention.

The bulk amorphous alloy sheet according to the present invention maytypically contain an amorphous phase of about 90% by volume or more,preferably about 96% by volume or more.

In experiments of producing an amorphous alloy sheet using theabove-described method and apparatus of the present invention, amorphousalloy sheets containing an amorphous phase of at least about 96% byvolume, even about 100% by volume were obtained. Typically, an amorphousalloy sheet of the present invention may contain an amorphous phase ofabout 96.0% by volume to about 99.9% by volume.

On the other hand, the bulk amorphous alloy sheet according to thepresent invention may also contain amorphous phase of about 90% byvolume or less.

There are no particular limitations on alloy compositions to be used ina method and an apparatus for producing an amorphous alloy sheet of thepresent invention, and an amorphous alloy sheet produced by the methodand apparatus. For example, there may be used amorphous alloycompositions such as Cu₄₇Ti₃₄Zr₁₁Ni₈ [S. C. Glade, W. L. Johnson: J.Appl. Phys., vol. 89 (2001) pp. 1573-1579]; Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ [M.Calin: Scripta Mater., in press (2003)]; Cu₄₇Ti₃₃Zr₁₁Ni₆Sn₂Si₁ [D. H.Bae, H. K. Lim, S. H. Kim, D. H. Kim and W. T. Kim: Acta Materialia,vol. 50 (2002) pp. 1749-1759]; Cu₆₀Zr₃₀Ti₁₀, Cu₆₀Hf₂₅Ti₁₅ [AkihisaInoue, Wei Zhang, Tao Zhang and Kei Kurosaka: J. of Non-CrystallineSolids, vol. 304 (2002) pp. 200-209]; Zr₅₇Nb₅Al₁₀Cu_(15.4)Ni_(12.6) [H.Choi-Yim, R. D. Conner, F. Szuecs and W. L. Johnson: Acta Materialia,vol. 50 (2002) pp. 2737-2745]; Zr₄₁Ti₁₄Cu₁₂Ni₁₀Be₂₃ [J. Schroers, R.Busch, S. Bossuyt and W. L. Johnson: Mater. Sci. & Eng. A., vol. 304-306(2001) pp. 287-291]; and Zr₆₅A_(7.5)Ni₁₀Cu_(12.5)Pd₅ [M. SherifEl-Eskandarany, J. Saida and A. Inoue: Acta Materialia, vol. 51 (2003)pp. 4519-4532].

Hereinafter, the present invention will be described more specificallyby Example. However, the following Example is provided only forillustration and thus the present invention is not limited thereto.

EXAMPLE

In this Example, a copper-based alloy with its chemical compositionpresented in Table 1 was used as a mother alloy. An apparatus shown inFIG. 2 was used. TABLE 1 Chemical composition of mother alloy ElementsCu Ti Zr Ni Sn Si Content (atomic %) 47 33 11 6 2 13 kg of a copper-based mother alloy was loaded into a high puritygraphite crucible and then maintained at a temperature of about 1,400°C. for about 60 minutes to be completely melted into a liquid phase. Acopper-based mother alloy melt thus obtained was discharged while beingmaintained at a temperature of about 1,200° C., and then transferredinto an inlet between rolling rolls of the strip casing apparatus

The rotation rate, surface temperature, and gap of the rolling rollswere about 2.0 cm/sec, about 20° C., and about 2 mm, respectively. Underthese process conditions, amorphous alloy sheets of 1 m in length, 10 cmin width, and 2 mm in thickness were prepared.

The non-crystallinity of the copper-based amorphous alloy sheets thusprepared was determined by X-ray diffraction analysis and the result ispresented in FIG. 6. As shown in FIG. 6, the amorphous alloy sheetsobtained in Example were in an amorphous phase that contained the smallvolume fraction of a crystalline phase.

The cross-sections of the copper-based amorphous alloy sheets obtainedin Example were subjected to an optical microscope image analysis andthe resultant cross-sectional microphotograph is presented in FIG. 7. Asshown in FIG. 7, no air gaps or cracks that may be caused bysolidification and contraction of a melt were observed in the alloysheets obtained in Example. In addition, the amount of an amorphousphase in the amorphous alloy sheets was evaluated. According to theevaluation result, the alloy sheets obtained in Example contained anamorphous phase of about 96% by volume or more. Therefore, it wasdemonstrated that the alloy sheets obtained in Example are excellentamorphous alloy sheets.

As apparent from the above descriptions, a method and an apparatus forproducing an amorphous alloy sheet according to the present invention isused in production of an amorphous alloy sheet of high quality, in whichthe generation of air gaps and cracks is remarkably reduced.

According to a method and an apparatus for producing an amorphous alloysheet of the present invention, an amorphous alloy sheet can be directlyprepared from a melt without using a separate process. Therefore, theamorphous alloy sheet, which has very high industrial applicability, canbe produced in large scale and at very low cost. Consequently, theapplication range of an amorphous alloy can be economically extended.

1. A method for producing a bulk amorphous alloy sheet, the methodcomprising: preparing a melt containing alloy components; feeding themelt directly into a gap defined between two rolls, which rotate inopposite direction to each other, and each of which is provided withheat exchange means; and cooling the melt at a cooling rate higher thanthe critical cooling rate for transformation of the melt into anamorphous solid phase, when the melt passes through the gap definedbetween the two rolls, wherein the rotation rate of the two rolls is inthe range of 1 to 10 cm/sec, and the gap between the two rolls is in therange of 0.5 to 20 mm.
 2. The method according to claim 1, wherein thestep of preparing the melt is carried out in an inert atmosphere.
 3. Themethod according to claim 1, wherein the heat exchange means is acircuit for flow of a cooling fluid.
 4. The method according to claim 3,wherein the cooling fluid is cooling water or cooling oil.
 5. The methodaccording to claim 1, wherein the two rolls are made of a copper-basedalloy containing material.
 6. The method according to claim 1, whereinthe temperature of the melt to be fed into the gap defined between thetwo rolls is in the range of 500 to 1,500° C., the surface temperatureof the two rolls is in the range of 15 to 30° C.
 7. The method accordingto claim 1, wherein the two rolls are arranged in such a manner that anangle defined by the horizontal and a straight line connecting therespective rotation centers of the two rolls, is in the range of 0 to 90degrees.
 8. A bulk amorphous alloy sheet prepared by the methodaccording to claim
 1. 9. The bulk amorphous alloy sheet according toclaims 8, which has a thickness of 0.5 to 20 mm.